Organization of supramolecular assemblies of fullerene, porphyrin and fluorescein dye derivatives on TiO 2 nanoparticles for light energy conversion

Abstract

TiO 2 nanoparticles were modified with a porphyrin derivative, 5-[4-benzoic acid]-10,15,20-tris[3,5-di- tert-butylphenyl]-21 H,23 H-porphyrin ( H 2 P- COOH), and fluorescein derivatives, 9-[2-(3-carboxy-9,10-diphenyl)anthryl]-2,7-difluoro-6-hydroxy-3 H-xanthen-3-one ( DPAX- COOH) and 2′,7′-difluorofluorescein ( FL- COOH). The dye-modified TiO 2 nanoparticles were deposited on nanostructured OTE/SnO 2 (OTE: optically transparent electrodes) together with nanoclusters of fullerene (C 60) from acetonitrile/toluene (3:1, v/v) using an electrophoretic deposition technique. The dye-modified TiO 2 composite electrodes [OTE/SnO 2/(dye + C 60) n ] have broad as well as high absorbance properties in the visible region, exhibiting the photo response under visible light excitation using I 3 - / I - redox couple. The incident photon to photocurrent efficiency (IPCE) for these electrodes increases in order: OTE/SnO 2/( H 2 P) n < OTE/SnO 2/( H 2 P- COO– TiO 2 ) n < OTE/SnO 2/( H 2 P- COO– TiO 2 + C 60). The IPCE value can be further improved by replacing H 2 P- COOH with a fluorescein derivative containing an electron donor moiety: DPAX- COOH ( DPA: diphenylanthracene). The maximum IPCE value (42%) is obtained for OTE/SnO 2/( DPAX- COO– TiO 2 + C 60) n under the bias of 0.2 V vs. SCE.